When is the Doctor?
The Third Doctor
To Fight Evil and acquire his freedom to travel (until The Three Doctors)
While the Third Doctor has a distrust of authority, he is an active crusader against evil and often leads the charge. He tries to see the best in his adversaries and encourages them to mend their ways (especially the Master), although when this fails he won’t hesitate to stop them. He dislikes aggressive solutions that leave no chance for a better outcome. He has a paternal attitude towards his companions.
The Third Doctor was exiled to Earth for the crime of interference with other worlds during his earlier incarnations. Stuck without a working TARDIS, he joined UNIT as Scientific Advisor and aided it against various alien threats. He was given his freedom after joining with his previous incarnations to defeat the renegade Time Lord Omega, although he frequently returns to Earth.